text:
How does Garmin Autoland for General Aviation aircraft work?
Garmin recently unveiled a new technology for their G3000 General Aviation avionics system, the Garmin Autoland. They claim it can safely and fully autonomously land the aircraft in case of pilot incapacitation.
Traditional autoland systems found on airliners use Cat. II or III Instrument Landing System (ILS) approaches to guide the aircraft onto the runway (and keep it on the centerline afterwards). But according to this article Garmin will not use ILS, but rely on GPS approaches only:

[t]he availability of a GPS approach with lateral and vertical guidance to the runway is also required when the system is considering various airports and runways.

Can GPS alone provide accurate enough guidance all the way to the runway including the flare? Usually RNAV approaches have higher LPV minima than even a Cat. I ILS.
As far as I know, the autopilot also cannot control systems like the landing gear, the flaps and the brakes, but all are needed for a fully autonomous landing. How does the Garmin system handle this?

The accuracy of GPS is better than required, but availability and the need for augmentation is critical. Garmin says "Autoland will soon be available on select G3000® system equipped aircraft: Piper M600 SLS and Cirrus Vision Jet", both model year 2020. These aircraft will have to expose the required controls to a communication bus.

LPV minima are often the same (200ft AGL) as ILS Cat I. Also, GPS (with or without augmentation) is usually ten times as accurate as the specification requires. "Usually" isn't good enough for routine use, but in an emergency, anything goes.

IANAP. I think that if I were flying with a friend and said friend became incapacitated, neither he nor I would care if the plane flared nicely and executed a greaser landing. If the autoland can get the plane on the ground well enough for me to walk away and him to be easily extricated and carted off in an ambulance, it's more than done its job. I sure wouldn't want the aircraft to be a write-off, but the computer's probably going to do a better job of landing it based solely on GPS than I would!

Interesting question. After some years, we have more information:

Can GPS alone provide accurate enough guidance all the way to the runway including the flare? Usually RNAV approaches have higher LPV minima than even a Cat. I ILS.

GPS (or GNSS in general) cannot be, alone and in normal condition, considered safe for autoland, but in a emergency condition like a pilot incapacitation... Well... It's better than nothing and it is worth to try. Indeed, Garmin website says (Ref):
"Autoland is designed to be used in emergency situations only and should not be used in nonemergency situations where the pilot is fully capable of landing the aircraft".
Tom Carr, Garmin's director of flight operations, stated (Ref):
"The overarching philosophy was, in our case, that the catastrophic event has already happened. So, we didn’t have to engineer-in redundancy."

As far as I know, the autopilot also cannot control systems like the landing gear, the flaps and the brakes, but all are needed for a fully autonomous landing. How does the Garmin system handle this?

In G3000-equipped aircraft, flaps and gears are "by-wire", so they can be overridden by the G3000. They are also equipped with an automatic braking system or custom solutions are developed for the specific aircraft (Ref1, Ref2). Indeed, if the pilot wants to get back the control, it must reposition flap and gear levers to the actual position (Ref (6:00)).


text:
Why is ISA Standard pressure 1013.2 not used for contour charts instead of QFF?
I am confused because QFF being actual mean sea level pressure is subject to change why would we use it for mapping terrain? Does this mean the height of a given terrain changes with the change in QFF? Tried to look for an answer for this everywhere but I couldn’t find any. Can someone tell me what am I getting wrong?

Where did you find this for terrain mapping? Are you sure you are not talking about weather maps?

@Bianfable maybe I should’ve worded this better. Let’s say the height of a hill is calculated from msl, we would use QFF to calculate it not QNH as QFF is more accurate and QNH is accurate only in a standard atmosphere. I understand this much but what I’m not able to grasp is the fact that QFF would change every now and then, what happens to the calculated height of the hill then, does it also change?

I still don't understand what you mean? The height of the hill above MSL is a fixed value measured with ground based instruments. It does not change with pressure or temperature or whatever. What exactly do you want to calculate with QFF now?

Welcome to aviation.SE! You might want to mention what QFF is for pilots who aren't familiar with it (e.g. in the US). The [tour] might be helpful if you're new to the site.

Maps and charts show true elevation, meaning tape measure altitude from the sea level. The way the mapmakers and chartmakers measure elevation has changed over time. Currently, I think GPS is prevalent. The way GPS computes elevation is depend on the WGS84 Geoid earth model. This modes surface does not coincide with actual sea level but GPS takes that into account. And today in most aeronautic related industries WGS84 is becoming a standart, which also includes maps and charts.
On the other hand altimeter provides height using pressure of air. QNH and QFF are the altimeter settings used to adjust for non-standard pressure and temperature, respectively. QNH is always provided to pilots and is the most prevalent. I have never heard that the QFF is used or requested by pilots.
As I said QNH setting only corrects for non standard pressures. It really assumes ISA temperature, 15C. So as you asked what happens if the temperature is not standard. Well someone needs to compensate for that and make correction.
Colder than ISA temperatures needs to be corrected for minimum enroute altitudes and obstacle clearances. Because the aircraft will be at lower true altitude than what altimeter shows, at colder temperatures. As for hot days, it’s less risky because aircraft’s true altitude will be higher than what is shown on altimeter. Only example comes to my mind is when you’re shooting an approach that has decision altitude kind of minimums. Since the aircraft will be higher than true altitude you may end up going around during real minimum IFR situations. However you will be on the safe side at hot temperatures, in terms of obstacle clearances.
As mentioned in that article; correcting minimum sector altitudes (MSA) and minimum vectoring altitudes for non-standard temperatures are ATC’s responsibility. In other cases, such as doing a published approach, it’s pilot’s responsibility.
That same article provides an excel at the end to use on the ground. Also some pilot operating handbooks provide charts to apply for altitude adjustments for non-standard temperatures. One technique for flight planning is to find the correction for the coldest temperature for  the day and apply that to whole flight. But that applies only to GA type flights really.
Not only that,  but also, there is this phenomenon called geopotential altitude. It implies that 1 altimeter-measured-feet at sea level is not equal to 1 altimeter-measured-feet say at 30,000 feet. And that’s because gravity is not constant as we climb. So the actual true elevation of the obstacle will always be slightly higher than what you see on your altimeter even when you’re side by side. However it’s really a small difference (less than 1%) and not a big factor at low altitudes where obstacles mostly live. [wp reference]

I understand this much but what I’m not able to grasp is the fact that QFF would change every now and then, what happens to the calculated height of the hill then, does it also change?

You measure the pressure at the top and at the reference point and use the temperature and humidity at that moment to calculate the height, write it down and be done with it. On another day the measurements will all come out different, but unless you make an error measuring or calculating, the height should come out the same. Because it is the same, after all. The accuracy won't be that great though. Also note that you need the temperature and humidity; QFF alone is useless without those.

why would we use it for mapping terrain?

I don't think anybody would, actually. Today you'd use satellite-based altimeter—that allows creating a complete height map in several passes and there are already such datasets including at least one free one—or GNSS. But before I believe a triangulation using theodolites was always more accurate, and to make a map you needed to do that to get accurate positions anyway.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Why would an aircraft's position be so inaccurate?
Normally when we follow an aircraft on flight radar, the track is very accurate and not noisy. I just clicked on an aircraft that has a very inaccurate trace. What might cause this?

It is parked outside 'STS Aviation Services'/'Monarch aircraft hanger' F62V+WV Birmingham so it could be the building blocking the signal.

Related (but not duplicate) question: https://aviation.stackexchange.com/q/2269/19

It's doing jumping exercises to keep in shape while it's waiting to be needed.

It's possible there are a few things going on here.
First, you are comparing what you see normally (flying aircraft) to one on the ground.
While flying, any inaccuracy in data is difficult to detect because the plane is (roughly) flying in a straight line, it would be hard to know if it was off by 100 meters in any direction. Under normal GPS conditions, 10-15m in the across track direction would be a standard amount of in the across track direction error in "normal flight". In the along track direction it will be more due to latency effects. (Along track error components are difficult to see on the map, because the error maps onto the track itself)
Second, ADS-B tracks are typically not mapped after the plane lands, so the noise isn't shown on maps.
Third, flights are usually viewed zoomed out- seeing a region or country or world on your browser. Instead you are zoomed in quite a ways- the entire map width in the screenshot is about 1800 feet (1/3 mile), and most of the tracks are contained within a 400 foot circle.
But what is really going on here can be seen by comparing your screenshot to Google Satellite Maps. We can see the airplane is inside of a building.
Since large aircraft don't spend much of their time inside buildings, the antennas aren't tuned for that (compared to, say, an iPhone).
I've kept the scale in the screenshot as well.

Because the GPS receiver antenna on top of the fuselage can't receive direct signals from above when the aircraft is in the hangar, all the satellite signals travel via reflections on the floor, walls and ceiling of the hangar. This makes the path-length different than the direct path, and hence the position is off. Not only is the path length different, due to the moving satellites, the reflection and interference pattern is shifting constantly, causing the GPS position to jump around.
You can see in the Flightradar 24 screenshot in the question that the flight ID of the aircraft was BOE1234. This flight ID is often used when Boeing aircraft are in maintenance.
Searching for historic tracks on Flightradar 24 with the callsign BOE1234 results in numerous similar position noise patterns:

Hi tedder42, nice answer. I used to work in ADS-B development, allow me to comment on a few of your points. On the first cause: In flight across-track accuracy  & noise is well under 100 m (more in the order of ~10 - ~15 meter). On the second cause, there are actually many airports with ground coverage, so this kind of errors would be seen. On cause 3: indeed, zoom in and noise seems to increase. case 4: you nailed it. Due to the GPS signal from the satellites coming through the door, bouncing of the floor, walls & ceiling, the resulting position is noisy. +1

If you want to see proof of this and you have a FR24 account that allows you to see historic tracks: look for tracks with callsign BOE1234 like the one in the question. This callsign is often used during maintenance of Boeing aircraft. You will find numerous aircraft parked in hangars which exhibit a very similar position noise pattern.

I've seen traces like this when a nearby cliff was messing with the signal.  GPS measures the distance to the satellites by the path the signal took.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Are four-engined airplanes calibrated to put out the same thrust for both their inner and outer engines?
Is there a slight difference baked into the aircraft's throttle control systems or are they always pumping out the exact same thrust as each other?

If the fuel control is hydromechanical (old engines) or electronically trimmed hydromechanical (not so old engines designed in the 70s and 80s), you set each thrust lever to achieve a target value on the fan RPM (N1) indicators or Engine Pressure Ratio indicator (EPR) indicators (for a pure jet).  Each engine will be set to its takeoff thrust setting, which should be the same for each since they are all the same model, but the thrust levers may or may not quite line up due to mechanical and other tolerances (there are limits).
On some modern airplanes with Full Authority Digital Engine Control, you move the levers to a detent setting, usually one for climb and one for take off, that is created by a roller running in a track inside the quadrant for each lever, that drops into a dip in the track; you can feel it click into place.
For takeoff you push them up through the climb detent to the takeoff thrust detent, so it's "click click". That position tells the FADEC computers to set takeoff power and the levers will all be perfectly lined up, the position being a function of the detents in the quadrant.  Of course, if it's got an autothrottle system, the computers take care of moving the levers as well.
In any case, the thrust settings for each engine should be the same, unless the airplane had engines with different thrust ratings inboard and outboard for some reason, and which would be an unpopular feature with most airlines.  I'm not aware of one.

Airbus and Boeing both use FADEC. Airbus has “detents”, Boeing does not.

When the levers are in the same position are the engine control systems calibrated in some regard for equal thrust, equal fuel flow, or something else?

You rig for synchronized levers with thrust/power equal, because that's what you are generally using to set power and that's what the crew will want to see.  On a turbofan, fuel flows and core rpm might vary a little bit for a given fan rpm from engine to engine depending on how worn out an engine is compared to its sister.  If two engines are set to the same N1 and the thrust levers have significant split, they may snag it, depending on how fussy the capt is.  One may snag it if they are split a quarter inch, another not until they are half an inch.

@MikeSowsun how does Boeing do it specifically as far as where to place a lever for say climb thrust?

We almost always use Autothrottle so it is done automatically. If for some reason you need to disconnect the Autothrottle, you just advance the thrust levers to get the desired thrust on the N1 gauge just like a regular aircraft.

thanks for the information.  I was mainly wondering about the difference between a pair of engines (say engines 1 and 4 vs engines 2 and 3) if they had identical thrust settings or if there was some reason to have one pair put out just a bit more energy than the other owing to there being a difference on where on the wing they are placed relative to the fuselage.


text:
Turbines in jet engines
I was reading this thread and in the answer, the person wrote "For example, the turbine blades are replaced after a set number of turbine cycles and/or after a set number of hours, which are lesser than the others."
What is the main reason for replacing the turbine blades?
is it the fatigue or deterioration of TBC?

Both, and it depends.  When a Hot Section Inspection is done, they are looking for mostly blade erosion beyond dimensional limits, and cracks.  Some cracks are allowed if the OEM's engineering determines they are benign (sometimes cracks form which fully relieve the stress that initiated them and the crack stops propagating - such cracks can be left alone, and the engine OEM will have clearly defined crack allowances and limits).
Erosion is mostly a function of how dirty the atmosphere is.  An engine running in the high Arctic that sees very little dust (outdoor dust close to the ground is mostly silica particles - sand paper without the paper) may run a very long time before significant erosion and the hot section might only have to be rebuilt due to burner can or blade cracking from operating cycles.
An engine running in the Middle East may only run half the normal TBO before blade erosion forces the engine off, made worse if an operator avoids using flex thrust to minimize engine demands on takeoff.
Then, some engines are more susceptible to erosion than others, depending on the compressor inlet design.  Turbofans with a stronger ram effect (good for overall efficiency and for windmilling after a flame out) suffer more than those with less.

And creep or high temperature stress-rupture.

how often are the blades replaced mainly due to deterioration of TBC?

You would have to look at the time between overhaul of a given engine; 5000 hrs, 10000 hrs, whatever.  They usually come off when the engine's ITT margin is gone and that is usually related to turbine efficiency losses from erosion.  Nobody just replaces blades.


text:
Can an ICAO contracting state charge money for NOTAMS?
does anyone know of any written icao rules where they state if a contracting state is allowed to charge money for the dissemination of NOTAMS? are products like notams and Local Aeronautical Circular messages supposed to be free for everyone? so that safety can be guaranteed ?

I don’t think there is a specific rule. In the US, NOTAMS are free. So are the majority of FAA documents and information like charts, handbooks, and manuals. If you want those same documents printed, there is usually a charge. If you get the documents from a third party vendor who got the information from the FAA, there can be a charge. And some information requires research on the part of the FAA or others (like aircraft ADs). There may be a charge for that.

Extract from ICAO Annexe 15 (Aeronautical Information Services):

3.5 Cost recovery

Recommendation.— The overhead cost of collecting and compiling aeronautical information/data should be included in the cost basis for airport and air navigation services charges, as appropriate, in accordance with the principles contained in ICAO’s Policies on Charges for Airports and Air Navigation Services (Doc 9082).

Note.— When costs of collection and compilation of aeronautical information/data are recovered through airports and air navigation services charges, the charge to an individual customer for the supply of a particular AIS product, either in paper or electronic form, may be based on the costs of printing paper copies or production of electronic media, and costs of distribution.

NOTAMS are issued gratis (free) as the information can be essential to the safe conduct of flights. The raw NOTAM is available to any member of the public, anywhere in the world online via the country's AIP (Aeronautiical Information Publication/Services) documents which are of a standard format. You'll probably have to register at no cost as a user though.
Click here for the FAA site
A company could charge a fee for processing the info thus obtained so as to tailor the NOTAM list and filter it in a manner suitable for a particular Operator. Or they could put it into a more user friendly format. It maybe noted that briefing areas have (computer) terminals dedicated to this linked to the official NOTAM server, and these terminals can have powerful filtering capabilities already provided by the issueing/distributing authorities.
ICAO lays down that safety related info should disseminated in such a way that there's no undue hindrance for the end user. Think of it this way - could the authority refuse this info to the pilot if it so happens that the subscription was not renewed on time due to any mundane reason?


text:
Incident & Accident Investigation
Does the airports have there own incident/accident investigation depts? or they are restricted to the NCAA/Safety dept only?

Does this answer your question? Incident & Accident Investigations

That question was closed @tsg

@GdD this is an exact duplicate by he same author.

Ah, I missed that detail @QuentinH!

@Hakimi, if your question was closed before because it lacked detail you aren't going to have any more success posting an identical one. Please add more detail to this can be answered, if you don't know what details to add feel free to ask in comments or chat.


text:
Can i get A&P course materials in .pdf format?
I would be very grateful if you provide me any material about A&P basic course for mechanics.

Go here for the PDF material.
Aircraft Handbooks & Manuals

thank you, but any other? i'm looking for materials being taught in academies

https://www.kingschools.com/aviation-courses/mechanics

I have friends who are currently in or have recently graduated from Aviation Institute of Maintenance. My local A&P shop has Jeppesen Maintenance Textbooks. Since the written knowledge tests come from the official FAA material, any school curricula that I have seen pretty well mirrors the FAA books. When it comes time to actually take the written test, I believe I will opt for the King School online curriculum. Then again, A&P for me will be just a hobby to work on my own plane. PS If you choose self-study in the US, you will have to document time actually working in a shop to get certificated

,grateful to you


text:
What is the exhaust from the end of jet wing prior to landing?
What is the exhaust from the end of jet wing prior to landing ? My guess,excess fuel from powering down engines.

Welcome to Aviation.SE! Could you provide a photo or video to illustrate what you're asking about?

Do you mean as shown on the images in this question? Or more like those in this question?

I suspect OP is talking about wingtip vortices.

See also Can these vortices be dangerous? with many nice images.

The only places where any fluid leaves a flying jet aircraft are the engine tail pipes, outflow valves and air cycle machine exhausts, and the auxiliary power unit exhaust, but that is usually only used on the ground.
None of these exhausts usually leaves any visible trail at low altitudes. The engine (and apu, if running; it is a small engine) exhausts contain a lot of water, but are very hot, so it remains a vapour; it only condenses at high altitudes where there is very cold. And the air from outflow valve—excess air leaving cabin—and from air cycle machine—air used for cooling—do not have any more water in them than the ambient air.
What on the other hand might leave visible trail is condensation is vortices behind wing-tips and sometimes end of flaps. This is just fog forming in very humid air due to decrease in temperature, like it might in the coldest hours around dawn, except here the cooling is local, caused by decrease of pressure that accompanies generation of lift by wings (this is called adiabatic cooling).
Regarding fuel, when the engine power is reduced, less fuel is simply pumped to the engines, so more of it stays in the tank. There is absolutely no reason to waste it by venting it anywhere—except for very, very rare case where the aircraft needs to return due to some malfunction, and needs to get lighter to avoid more damage on landing; but this intentional fuel dumping is always done at high altitude so the fuel evaporates before it could get to the ground and contaminate it.


text:
Turboprop vs Turbofan: How to compare Specific Fuel Consumption
I understand that Turboprop engines have a lower Specific Fuel Consumption (SFC) than Turbofan engines, on average. I want to see this for myself by analysis, ideally by comparing values of SFC for typical turboprop engines vs turbofan. As turboprop SFC is usually given as the Fuel Consumption Rate / Power, and turbofan SFC is given as Fuel Consumption Rate / Thrust, it is tricky to directly compare them.
For a given airspeed and altitude, I want to show that a turboprop engine will require a lower rate of fuel consumption to produce a given amount of thrust. Is there a way I can show this without going into too much detail on things like blade pitch, thrust coefficient etc.
Ideally, I want to compare SFC of turboprop engines with that of turbofans, and show that the SFC for turboprop engines at a given thrust is lower.
Thanks

Well, propellers deliver thrust and turbofan engines deliver power to the fan axis, it is just a matter of choice.
Finding the thrust that a propeller generates at a specific airspeed and altitude, can be derived from the drag of the whole airframe in those conditions. Statistically, this sort of data can be found in reference books on pre-design of aeroplanes, such as Synthesis of Subsonic Airplane Design by E. Torenbeek. If we take a generalised approach:
$$D = C_D \cdot ½ \rho V^2 \cdot S \tag{1}$$
$$C_D = C_{D0} + \frac{{C_L}^2}{\pi A e} \tag{2}$$
$$C_L = \frac{2W}{\rho V^2 S} \tag{3}$$
So total drag follows from:

design factors weight W, wing area S, wing aspect ratio A, Oswald factor e.
environmental factors airspeed V and air density $\rho$

For the generalised $C_{D0}$ of aeroplanes, from Torenbeek page 149:

So you can use all of this to compute propeller aeroplane specific thrust. But the exercise will be futile, because:

The engine of a turbofan looks remarkably like that of a turboprop. In fact, they are both turbine engines, powered by the Brayton cycle. Similar size and design engines deliver very similar gas generator power to the [fan or prop] axis.
Turbofan engines tend to larger than turboprop ones, generating extra efficiency due to less boundary layer effect and more uniform internal flow.
Speed is of the essence: at turboprop speeds, turbofans are not very efficient. At turbofan speeds, turboprop cannot deliver enough thrust due to propeller tip drag divergence.
Turbofans utilise more of the hot exhaust flow for thrust generation due to the higher required flight speed. Lower efficiency, higher thrust.


text:
How to calculate bending moments and shear forces on a wing?
I am trying to create a MATLAB script to plot the Bending Moment Diagram (BMD) and Shear Force Diagram (SFD) as a function of spanwise distance, x, along a wing from the wing root (x=0) to the wingtip (x=b/2).
I will be considering the case where the lift generated by the wing is 2.5 times the weight of the wing (so n=2.5).
The three main forces I plan to consider in this analysis are:
1) The weight of the engine (Point load)
2) The weight of the wing (uniformly distributed load)
3) The lift generated by the wing (bell loading distribution)
My question is this: how can I set up an equation for the bending moment and shear force as a function of spanwise distance, x, despite a non-uniformly distributed load being considered in combination with a point load and a uniformly distributed load?
The classes I have taken at college have only covered BMD and SFD for uniformly distributed loads, so I am a bit confused as to how to go about setting up a numerical model for a non-uniform load.
Thanks a lot.

Could you perhaps add a force body diagram to your question? And could you approximate the non-uniform distributed loads force equivalent via integrating, and the location via the centroid?

You can readily solve this analytically using superposition of your load cases. I can highly recommend Mechanics of Solids by Roger T. Fenner. The chapter on beam bending will have all you need and more. But feel free to use numerical methods if you just want an answer instead of fully understanding the underlying physics.

I would highly recommend to discretize your problem, for two reasons:

You are using Matlab which is most suitable for a discrete approach anyways
More complex load cases will make analytical continuous modelling difficult. This is why these kind of problems are typically solved numerically

So now the question how can we discretly regard this problem? For the wing bending moment, this is pretty straightforward. First of all, lets make a small sketch.

The process of discretization is now to look at equally spaced points of the wing seperated by the distance Δd. I call them discretization points. I have labeled them in the following sketch as a vertical line numbered as 1, 2, 3 ... until point i.

What you need to do now, is to calculate the force acting on each discrete point. This part in turn is divided into two parts:

Calculating the exact shape of the different forces: Therefore force of motor weight, force of the wing structure and as a function of these two, the bell function of the lift
Integrate the wing lift force and structural weight force from discretization point k-1 to point k.

Now you have the exact weight acting on each point k (simply the integration of the wing lift force and the structural weight force from point k-1 to point k). Calculating the bending moment is now straightforward. For example, the bending moment at point i-1 is just the force acting on point i times the distance from point i-1 to i:
$$ M_{i-1} = i \cdot \Delta d \cdot F_i $$
the bending moment at point i-2 is now therefore:
$$M_{i-2} = 2*\Delta d \cdot F_i + \Delta d \cdot F_{i-1}$$
and so forth and so on.
The shear force at these points is even simpler. It is just the sum of all forces at the different outboard. So for example at point i-2:
$$ F_{i-2} = F_i + F_{i-1} $$
You can see that this type of equations can be easily programmed in Matlab. If you program this a bit cleverly, you can even play around with different values of Δd, which enables you to see the effects of discretization.
Hope this helps. If you need more help with the code, feel free to ask.

welcome to community.

To include the point force from the engine mount you will need to use a Dirac delta and a Heaviside step function to add in the moment caused by the engine.
The Dirac delta multiplied by the engine weight will model the force, and once you integrate over the span once to obtain the moments it naturally will turn into the Heaviside step function.


text:
How big is the TP400-D6 turboprop installed on the A400M?
I am trying to re-create the A400M TP400-D6 engine in CAD, mainly the nacelle and propeller, yet I can't find any detailed dimensions for it.

Europrop specifies a 0.92m diameter for the TP400-D6, so I assume the nacelle used on the A400M is roughly 2 meters tall and 1.5 meters wide - is this a reasonable estimate? Or even better, where can I find more information on the actual size of the A400M nacelle so I can accurately model it in CAD?
Thanks a lot.

According to the MTU Aero Engines technical data of the TP400-D6:

Propeller diameter: 209.8 in

(mtu.de)
That is a propeller diameter of 5.33m. I also could not find more details about the nacelles, but one can estimate the size from a photograph. I used this image from aviationtoday.com, which shows the aircraft from the front. With the known propeller diameter, I estimate the nacelle to be about 1.2m wide and about 1.85m high:

I don't think it is possible to derive more precise numbers due to the inaccuracies resulting from the perspective.


text:
Use of a leased/rented aircraft for business use and flown by a company employee
I believe this is allowed under 91.501 but not sure what the definition of "operated by the company" is.
A pilot with ATP,MEL,MEI is employed by the company as its corporate pilot and paid a salary.
The pilot finds a twin engine aircraft owned by another company/individual that is not used in any commercial operation. A per hour dry rate has been establish for this aircraft.
The purpose of the flights is to fly company employees to meeting sites at multiple company locations.
Can the company pay the dry rate plus fuel for use of this aircraft?
Can the pilot operate this aircraft legally under part 91 based on compensation as a salaried employee?

If I understand the question, the company wants to dry-lease a plane so the corporate pilot can fly company personnel on company business. I wouldn't think that the fact that the corporate pilot is the one who found the plane and arranged the lease would have any more/less bearing on the legality than if someone who flies a desk for a living found the plane/arranged the lease. IANAL, but I think that is how many/most corporate aircraft are operated today. Some are company owned, but I'd imagine the majority are leased.


text:
What modifications/upgrades were done to US MD-80 fleet?
I have often heard stories about how most of the MD-80 fleet that are being retired in the US were modified and upgraded.
What were the modifications or upgrades done?

Can you link some of this stories?

It won't be much mechanical.  It's going to be almost all avionics/electronics upgrades, like changing from steam gauges to flat panels, or sometimes structural mods and reinforcements to allow operation to higher hours without unworkable inspection frequency requirements.


text:
Difference between general visual inspection and pre-flight check inspection
I know the definition of general visual inspection (GVI) but I cannot understand the differences (if there are) with a pre-flight check inspection.
I am new in the field and I am not a pilot (don't worry...) but I would be glad if anyone could clarify this for me.
Thanks.

A GVI is a maintenance procedure that has to be performed by a mechanic qualified to do so, to satisfy a Maintenance Program requirement, and which will require a maintenance release to be signed off.
A pre-flight inspection is an inspection performed by a pilot in command (or someone delegated by the PIC - like a First Officer, or a mechanic) to satisfy the PIC that the aircraft is safe for flight.
The pre-flight, being a look-over to make sure nothing has fallen off, is dribbling fluid, or is flat, is going to be more superficial than a GVI and usually doesn't involve getting your hands dirty (at airlines it's usually done by the First Officer while in uniform) and normally doesn't involve opening access panels or doors (but could).  Also the pre-flight is a whole-aircraft once-over while a GVI is usually system or zone specific in keeping with its Maintenance Program objectives.

Preflight may consist items which are GVI in its nature. But the difference is how regulations treats such inspection (preflight). As per Commission Regulation (EU) No 1321/2014 Pre-flight is not considered to be maintenance:

(h) ‘maintenance’ means any one or combination of the following activities: overhaul, repair, inspection, replacement, modification or defect rectification of an aircraft or component, with the exception of pre-flight inspection;

and thus:

(d) The pilot-in-command or, in the case of commercial air transport, the operator shall be responsible for the satisfactory accomplishment of the pre-flight inspection. This inspection must be carried out by the pilot or another qualified person but need not be carried out by an approved maintenance organisation or by Part-66 certifying Staff.


text:
Is there a minimum amount of time an airline has to leave between using two identical callsigns?
Does anyone know if there is a minimum time that an airline has to leave before reusing the same callsign?
I have noticed that airlines reuse callsigns, they usually leave a day or two between reusing them. I'm just wondering is there any regulation on the minimum amount of time that must pass before they can reuse the same call sign again?

Usually the call sign for a flight is the airline plus the flight number. Many, many flights run the same number daily, which means that the call sign is reused daily. Do you have some reference that they "usually leave a day or two between reusing them"?

Related: How are duplicate call signs dealt with?

@FreeMan - thanks for that. No hard numbers, just something I have noticed looking at ADS-B networks. I'm developing an application which monitors flight cycles and want to know if there is any regulation regarding the legal amount of time that has to pass before a particular call sign can be reused?

@Freeman what do you mean by flights reuse a flight number? As I explained in the comments on the answer, whilst one flight number can cover a multi segment journey, there are rules and conventions on that. And that it is really rare to see multiple allocations of the same flight number.

@Freeman it's really rare to see the same flight number used with more than 8 segments and even 4 is unusual. So I'd really surprised if it was common for the same call sign to pop up more than 4 times a day.

Airlines work to make sure there is no duplicate callsigns in the same area at the same time. But there is no regulation for time between the reuse of a callsign.
They achieve this by either a callsign being used only once per day or with enough time between flights that there is no chance for both flights in the air at the same time.
The issue comes if two aircraft are in the air with the same callsign. The air traffic control systems will not be able to tell an ATS message (e.g. DEP, EST, CNG) for one aircraft from an ATS message from the other aircraft with the same callsign. Plus many other issues.
So if an airline needs to use the same callsign twice, like if the first flight is really delayed, they tend to append a letter to the end of the callsign, for example UAE212 becomes UAE212C.
Not asked but for completeness; there is also a risk if the callsigns are close but not the same, for example United 222 and United 232, there could be confusion between the aircraft over the radio. In these situations the air traffic controller can change the callsign to make sure there is no confusion. This could be while they are in the same airspace or for the entire flight.
The risk of callsign confusion has been documented many times in many incidents around the world. e.g. May 10, 2004 near Julian, California Callsign Confusion

Generally speaking for scheduling airlines will only use the same flight number once per day. Its extremely unusual to see the same flight number scheduled at an airport more than once per day, though occasionally it happens during DST changes. The most common reason for flight number reuse on the same day is delays. (same day being the 24 hours 0:00 to 23:59 local time).

There are examples where the same flight number with stops is operated with multiple aircraft, and while not friendly to customers, it’s at least theoretically possible for the second aircraft to depart before the delayed first aircraft lands.

@user1937198  The same flight number at the same airport on the same day would be quite rare, but the same flight number can operate several times during the day, with the aircraft flying from A to B, then B to C, then C to D, and perhaps on to more cities beyond that, all with the same callsign.  In domestic US operations, that's not at all uncommon.

@Ralph J In scheduling parlance, that's the flight number being used once, calling at A then B then C then D. This does not need disambiguation unless delays cause a later segment to depart before an earlier one. Disambiguation would only be scheduled if the next days flight departed A before the previous day's flight arrives at D. Since these flights tend to be short haul and during the day that's pretty rare.

@StephanS that still counts as a single flight number for scheduling purposes. Flight numbers are more closely tied to fare structures than how physical planes actually operate. In the case of delays either a planed or an unplanned airplane switch could result in an unplanned operational suffix being needed.

They will use a flight number once per day, but that flight number may have multiple segments, each of which may be physically flown by a different aircraft.

If it's two segments of one flight number, there might only be a 15 minute gap between arrival and departure. If it's a different allocation of the flight number, they will almost always wait until midnight rolls over.


text:
Is there any bibliography for triplane aircraft design?
I've been tasked with designing an RC aircraft that has the greatest lift force for a specified wingspan, total length and takeoff velocity, and thus have been studying the different wing configurations that could be used.
I've had ease in finding methods for designing more common configurations (using books such as Snorri Gudmundsson's and Jan Roskam's), even biplanes, however it seems there is no method specialized for estimating the aerodynamic coefficients for triplanes, which to me seems to be a very promising way to increase wing area with the given geometrical constraints. There are methods for biplanes such as Munk's General Biplane Theory, but not triplanes.
I've managed to use the XFLR5 software for simulating the configuration (wings and vertical stabilizer only, though - I've had to use the elevator as the third wing). However, I've learned it's not good practice to rely solely on a single method's results for obtaining the aerodynamic coefficients, and without some sort of semi-empirical method to compare it against, I'll unfortunately have to scrap that possibility.
If there are no such equations, can the biplane methodology be adapted in any way for a triplane? I've found two NACA reports comparing biplane and triplane wind tunnel results, but haven't managed to fiddle with the biplane equations and get accurate results from them.

You could compare a biplane with a monoplane of the same planform and obtain a lift differential (which will be less than twice the monoplane lift). Then just repeat that differential for each extra wing in the stack. Why not go for a quadruplane or even more?

Something like Munk's "General Biplane Theory" proposed "k" coefficient to convert a biplane into an equivalent monoplane? Perhaps generating multiple triplane planforms in XFLR5 would allow for curve fitting such a coefficient for a triplane instead for a rough estimate of the final lift coefficient slope?


text:
Why don't commercial airliners use variable sweep wings?
I know they're not used in military aircraft because it decreases the stealth factor, but why don't commercial plane manufacturers make variable sweep planes?

Variable geometry is not used in commercial aircraft design for the same reason that they initially became popular in the 1960s but have fallen out of favor in more recent times: any kind of aerodynamic performance gains associated with the design is not worth the additional weight increase, and subsequent decrease in payload, associated with variable sweep wings.
There have been attempts to do so in the past. The ill-fated Boeing 2707 SST was supposed to make use of swing wings but designers could not achieve their payload goals with the design.   Usually more judicious application of aerodynamic principles during initial design is far more advantageous then beginning to design out right with a swing wing.

May be worth adding mention of additional maintenance overhead and associated risk. All designs for all things are a long series of compromises. Commercial Aircraft compromises aim towards safety, cost effectiveness, and high up-times. Variable sweep wings run counter to all of those goals.

To enlarge upon Carlo's answer, variable sweep was intended to permit subsonic and supersonic flight. Since supersonic passenger flight is not viable from an economic standpoint, airplane designers do not have to accomodate it in their wing designs, and can support the low-speed flight regime with slats, leading edge droop, extensible flaps and drooping ailerons- which can all be incorporated into a fixed sweep wing which is otherwise optimized for subsonic cruise conditions.

The British designer Barnes Walls (famous for his bouncing bombs) developed a swing-wing airliner concept during the postwar period. It was a radical rethink which he regarded as no longer an aeroplane but instead he called it a wing controlled aerodyne. He flew a series of radio-controlled UAVs, Wild Goose being the first and Swallow the second.
They were aerodynamically exremely clean, Wild Goose being just a streamlined fuselage like a mini airship (he had also designed the R100) with two movable wings. There were no other control surfaces or tail plane. Swallow was a higher-speed development with its fuselage in the form of a delta-shaped lifting body and with swivelling engines on the wing tips.
Although he proved the aerodynamics, there were still a lot of technical unknowns. The cost and risk of developing such a brand new concept into his proposed non-stop England-Australia airliner was too much and funding ran dry in 1957.


text:
Airliner headlights flashing alternately
I live in Portland,Oregon.  I watched a large jetliner coming into the airspace heading to the airport.  The red,green and tail lights were normal. But the headlights were blinking alternately.  I have never seen that in all my years watching the sky. Is there a reason for the alternate blinking?Emergency onboard?

Does this answer your question? Is it unusual for an aircraft to flash its landing lights in sequence?

Some modern landing lights have a pulsating or alternating mode. It's just for being recognized more easily, has nothing to do with an emergency.
A constant white light heading right for you over a city full of lights doesn't get as much attention as a pulsating light which gets bigger each time as you get closer :)
Here is one example: https://www.preciseflight.com/pulselite-pulsing-aircraft-lights/
and their video:

Thanks. It just seemed unusual.

What you were likely seeing is the wingtip strobes which are white and flash alternatively. Aircraft don't have "headlights" per-say but they do have landing lights which do not flash by design but can be flashed manually.

The proposed duplicate suggests landing lights can flash. Or did I misinterpret that?

@PerlDuck landing lights can be flashed manually and its possibly thats what was seen but it is also possible it was the flashing strobes which flash by design. Ill edit my answer a bit to elaborate on the landing lights needing to be flashed manually.

I edited my reply as well, I've seen many videos of aircraft that do have pulsating landing lights and no you don't have to manually flash them.


text:
is it mandatory you put a ground cable for airbus aircraft parked over night?
is it mandatory you put a ground cable for airbus aircraft parked over night

I think you should ask Airbus, I always find it worrying that people working around (or on) real aircraft search for technical solutions on an online Q&A site

@DeepSpace Who says OP works with aircraft? Could just be an interested enthusiast.

I didn't even know ground cable exist. Do you have any illustration?

He means running a grounding wire from an earth connection point in the ramp surface to a grounding lug usually somewhere around the landing gear bays.  Like when fueling.  You see lots are airplanes parked without being grounded.  I don't think it's mandatory unless there is fueling going on.

thank you John for clearing my issue

https://www.google.com/url?sa=i&url=https%3A%2F%2Fcode7700.com%2Ffueling.htm&psig=AOvVaw0bBdnfcMTJS5MjZkUV6s6H&ust=1583352367452000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCNDEiK-N_-cCFQAAAAAdAAAAABAD


text:
What to do as an international student without a driving license that is needed for PPL Training in Germany?
I am required by the Luftamt Südbayern to provide information from the driving suitability register from the Federal Motor Transport Authority in Germany but I do not have a German driving license as I am an international student.
Anyone with any ideas as to how I should approach this?

You do not need a driving license to request information from the German Register of Driver Fitness.
The Kraftfahrt-Bundesamt has a website in English with information on how to request your information free of charge: https://www.kba.de/EN/ZentraleRegister_en/FAER_en/Auskunft_en/faer_auskunft_inhalt_en.html?nn=642934

Thank you very much for the help. I appreciate it.


text:
Why don't aircraft have DME that can automatically convert the slant range to ground range?
Knowing that $a^2 = b^2 + c^2$ where $a = \text{slant range},\ b= \text{ground range},\ c = \text{height}$.
Why can't the DME equipment which calculates the slant range then just convert it to the ground range? Surely for navigation and position fixing knowing the actual ground range would be more useful? Is there a practical reason why the slant range has stuck?

Unless you're really close to the station, the difference isn't big enough to matter. The DME signal is very simple, and simple systems are inherently more reliable.

This simply is not mathematically possible (as well as being not KISS, and not in number domain).

If you're in a plane flying at 5,000 feet and the DME indicates you're 25 miles from the station (assumed to be at sea level), your actual distance to the station is 24.98 miles. How critical is that 100 feet?

There's no accurate and simple way to know the height above the station in order to do the calculation with the existing equipment. Altitude is not an indicator as the DME station may be above sea level. If your airplane is at 15,000ft and the station is at sea level you'll get one answer, if the station is at 10,000ft you'd get a completely different result, and mistakes could compromise safety.
The only way your proposed system would work is if the DME device had a complete database of every station height and altimeter readings, which would require upgrading the DME devices at great expense. I don't think anyone is interested in that when you can have GPS for a lot less money.

The alternative is if each DME station broadcast its elevation.  However, its just not necessary: DME is used to inform pilots when they're getting close to a station, the precision of slant-range adjustment just doesn't add much useful information.

@abelenky Broadcast how, to what? That'd be an entirely different standard.

@Dan On a subcarrier, same as VORs send their Morse code identifications. To the DME equipment on the airplane, so it could calculate the slant range. It would be a new version of the same standard; existing DME equipment would ignore the subcarrier and continue to function as normal.

You could encode the altitude in the signal for sure, then you'd have to modify all the stations as well as the receivers which would make it even more expensive.

@GdD: Using a subcarrier in a way that's backwards compatible allows gradual rollout with new planes and when ground stations are being replaced anyway, eventually fixing the "problem" for hypothetical DME2.0 capable planes when approaching ground stations which have upgraded to DME2.0 transmitters.

When are the ground stations being replaced @PeterCordes? Seriously, nobody is going to spend money on that.

@GdD: eventually in the long term, as gear wears out?  Or as a minor cheap upgrade without replacing the power amplifier / antenna possibly.  I didn't say it would be fast.  But if it was something worth doing (which it apparently isn't), some ground station operators would presumably be willing to spend the money while some wouldn't be, and backwards compat makes that not a showstopper.  That was my only point (plausible and technically feasible), not that this was something that has any chance of really happening.

Fair enough @PeterCordes. I think it's agreed it's technically feasible.

You have to realize that the DME is a justified and ancient nav system. When it was concieved, it was chosen to keep it simple, for obvious reasons.
As it is, it does not have to communicate with any other system, making it a very reliable stand alone device.
There is no need to create a "DME 2.0", we already have gps and other more sophisticated systems to tell us how far we are from any given point in space.

a justified and ancient nav system Fitted to the Last Plane to Transcentral?

@Graham: It's Trancentral, as in Trance music.  But yes, and its departure time is 3 am.

@PeterCordes Oops, typo. :)  All aboard, all aboard...

Transcendental

In other words, when DME was invented, avionics didn't have computers. And now it's irrelevant.

authors: Bob Jarvis - Слава Україні


text:
Why don't planes fly directly to their destination?
Here is the flight path for B62554 from PBI (Palm beach) to JFK. This flight almost goes back on itself when off the coast of South Carolina.
I was wondering why this flight takes such a contorted path? Another example is B6242 from Havana to JFK, which similarly diverts out to see when near New Jersey then comes back at an almost 90 degree angle.

Note that flights do not always follow the same route.  For example, FlightAware has the last two weeks of flight paths for JetBlue 2554 (scroll down to the table listing "Past Flights" to find them.)  The flight on 2020-03-21, which you've included in your question, has several jogs & diversions.  The flight on 2020-03-20 was much straighter.

There are many reasons why planes don't fly direct to their destination.

Mountains (for smaller piston aircraft)
Traffic capacity and traffic flow considerations for the ATC center
Weather along the route
Preferred airway routings

For an analogy, cars don't drive direct to their destination for the same reasons.  Roads, I would venture to guess, would be preferred routings to your destinaiton.
There would be a traffic jam if everyone wanted to get to the closest airport for the Olympics at the exact same time.  Traffic flow considerations would dictate planes slow down or fly a different routing or wait till there is a time slot for them to land at their destination.


text:
Does counter-rotating propellers on multi engine airplanes have critical engine?
I read from most of the article and books that counter-rotating propellers multi engine airplanes do not have critical engine, but it just happened to my friend who did his Commercial Multi Engine Rating check-ride that he answered there is no critical engine on counter-rotating propellers and the examiners failed him.
And one of the instructor said that he should answered both engines are equally critical.
 is there any terms that stated that counter-rotating  propellers has both engione critical?

It's just a matter of semantics.  "There is no critical engine" simply means that neither engine is more, or less, critical than the other.  Which is the same thing as saying "both engines are equally critical."  This is a talking point to clarify during the exam, not failure criteria.  I would file a complaint about this if it was the only reason for failing...

The term "critical engine" can actually refer to two very different factors:

P Factor
Engine driven accessories, depending on the airplane and how it's configured.

A twin with counter-rotating propellers doesn't have a critical engine from a controlability perspective, but very often there are important engine driven accessories, like hydraulic pumps, vacuum pumps, generators, etc. that are only installed on one engine, and if you lose that engine, well it's more of a problem than the other one.
So you may lose the left engine and it has no effect on control or performance compared to the right, but that engine has the only hydraulic pump, so now you have to do the engine-failure-on-a-missed-approach song and dance, all while hand pumping the gear up.  Gets pretty busy.  In such a situation I'd consider the left engine more critical than the right one even though it's not a stick-and-rudder problem.
I think that's what the examiner was looking for.

Excellent points, I didn't consider that in my comment above.  Perhaps there is more to the story on this particular exam failure...  Still, you would think the examiner would have explained this to the examinee as the specific reason for failing.

Yes agreed thanks.  I think part of the problem is students are learning on newer twins with dual everything and are unaware that there are older twins with single accessories that create that situation.  My fav is the B-24, which only had one hydraulic pump, on engine #3.  Shutdown that, and you lose your gear hydraulics and your brakes.  They had a procedure where the waist gunners would hook their parachute harnesses to the waist gun pintle mounts or some other convenient structure and deploy them on landing to help slow down.

As an addition to John K's answer - There are twins that have propellers on both sides rotating 'outwards', thus both are critical aerodynamically.
Of course another possible answer is the critical engine is the one that that is still running after one of them fails.


text:
Why were german pilots more successful on the eastern front than the western front?
I was wondering why big german aces shot down the most enemy aircraft while fighting on the eastern front. Is this because the soviet pilots were undertrained, or their flying machines were inferior? Is it something else? You see all these German aces that have shot down 100+ aircraft and most of them fought on the eastern front. Why is that?

The Germans flew until they were killed and many were in combat for nearly 4 years straight.  Allied pilots flew until their tour was completed.

If we're talking about the scores of individual aces, rather than overall totals, it's probably tactical. The leader would fight purely offensively and rely on his subordinates to protect him, and thus claim nearly all the kills for the squadron.

Several factors.  The ones you mentioned, plus the different purpose of most of the Soviet aircraft and the longer flight career of German pilots on the Eastern Front.  Beyond that was the fact that, early in the war, the Germans enjoyed near-complete air superiority (reinforced by their superiority in other factors).
As you note, at the beginning, most of the Soviet aircraft were inferior to the German ones; some of them were ten or even fifteen year old designs (or even older -- one squadron, known as the "Night Witches", flew biplanes into 1943), while the Germans flew new designs, either late pre-War or fresh off the drawing board.  The newer aircraft were faster, more robust against damage, carried heavier loads and more/larger guns.  This aircraft design deficit was reduced and possibly even reversed later in the war, but by then the Germans were on the defensive, being pushed back week by week.
The German pilots, at least early in the war, were far better trained -- theirs was the best air force on Earth in 1940 (though they started to run out of good pilots later in the war, because they had a far smaller population to draw replacements from and were resource limited in building aircraft, both for combat and for training).
Further, the German aircraft that the aces flew were dedicated fighters, designed from the ground up to destroy other aircraft in the air.  The BF-109 and Focke-Wulfe 190 were superb airplanes for the day.  The Soviets, on the other hand, especially early in the war, had a heavy preponderance of ground attack aircraft, and their primary mission was to destroy German armor, infantry, and supplies.  This made them sitting ducks for the German fighters and fighter pilots.  Further, there were lots and lots of those differently tasked and outdated Soviet airplanes -- the Soviet Union had more than twice the population of Germany and tens of times the landmass and resources; that gave them the ability to do the air equivalent of "human wave" attacks, which would still succeed even after a "turkey shoot" by the Germans.
Because of the disparity in pilots and aircraft, the German pilots lasted a great deal longer on the Eastern Front, where they weren't flying against the elite of nations larger than their, who hadn't had a decade or more with no powered aircraft and who had P-38s, P-47s, and P-51s, Hurricanes and Spitfires to pit against their aircraft.  The Western Front pilots had a strong tendency not to come home, even in the early years of the War, and much more so after the Normandy invasion.
Additionally, especially after the first winter of the Russian invasion, German pilots stayed on the line until they were physically incapable of flying -- either dead, or seriously injured (loss of eyes or limbs, for instance), or shot down behind lines and captured.  As noted in comments, also, there was a tactical difference, with German squadron leaders often flying without any thought for defense, trusting their mates to protect them while they simply destroyed as many enemy aircraft as possible, and this worked better against the relatively less experienced pilots in the Soviet forces.

I agree, @ymb1 but I'm at work and don't have time between tasks to dig up a bunch of quotes and links.

The USSR had nowhere near 100 times the population of Germany. While exact figures are hard to come by, or even to define (do you include Austria's population in Germany, or the recently conquered Baltic republics as part of the USSR?), rough figures are 160-180 million for USSR, 70-80 million for Germany.

Thanks, @jamesqf that one slipped by me as I was typing.  Area is close to 100x, but I've change it to "tens of times" and population to "more than double".

@ZeissIkon: Thanks! Just what I needed!

It's a big simplification (bordering on incorrectness) with the airplanes. It is more or less applicable early in the war, but by about 1943 there was no shortage of new 'dedicated fighters', some of which (La-5/7, Yak-3) were, at least nominally, quite on a par with contemporary German fighters, and superior to some Allied designs (such as Hurricane), especially at lower altitudes where most of the fights on the Eastern front tended to be. Overall, the result has much more to do with pilot training, as well as with having massive air superiority in the first half of the war.


text:
Why does camouflage make some planes fly slower?
Why does camouflage decrease some airplanes' speed? I have noticed that some planes fly slower with camouflage than without it. For example, when the RAF applied camo on the P-51 Mustang, they noticed that it was 8 mph (About 12.87 km) slower than without it. This is why the Mustang usually had no camouflage on. My question is why did the camouflage make it go slower? Did/does this apply to other planes too?

Same reason gliders keep their wings waxed.  It wasn't the camo per se, it was the dull matte field-applied paint finish that included all sorts of imperfections, and to a small degree, the weight of the paint vs natural finish.  At a microscopic level, the surface of the matte finish was much rougher than a gloss or unpainted metal surface.  The microscopically rougher surface would have a stronger ability to inhibit air molecules flowing right against the surface (skin friction).  Add to that the surface imperfections introduced by the typical wartime spray-and-get-it-out-the-door process, vs smooth bare aluminum.
Think of the inhibiting effect on wind velocity close to the ground of a forested area vs a grassy plain, and shrink it down to the micro level.  The effect is most pronounced where the flow is relatively smooth, or laminar against the surface, which is most areas there the cross section is getting fatter (leading edges of wings and control surfaces, the nose, etc).
The Mustang would suffer a bit more than others from this with flat paint because of its (somewhat) laminar wing that had a maximum thickness well aft, which means it would have more surface area that is sensitive to skin friction, than a non-laminar wing aircraft like a Spitfire or Typhoon.  So if the Mustang was penalized 5kt with flat paint, a Spitfire might have only been penalized 3kt because it had less surface area that was (relatively) laminar in the first place.

In the early days of military aviation, there were several accidents caused by air force squadrons painting their own designs and logos on "their" aircraft, with unexpected consequences for the aerodynamics. As a result, in the UK decorating aircraft wings and control surfaces was prohibited, though other decorations were allowed as morale-boosting activities.

@alephzero -- I have never heard that before.  I would love to see more details incorporated into either an answer to this question or perhaps into a self-answer to a question of your own asking.

Almost sounds like a less extreme case of frost on the wings.

It's primarily all about matte vs glossy finish.  Normally a camo paint scheme would not be finished in a glossy finish as this might flash in the sunlight.  A matte finish is rougher and thus has more air resistance than a glossy finish.  The roughness is on a scale that is much larger than microscopic, but not obvious to the naked eye.

I don’t know if it’s the same with the paints used on aircraft, but on vehicles, the small-scale roughness of matte paint is often visible to the eye close up, and certainly perceptible by touch.

Future edit: modify according to above comment that roughness of a matte finish is visible to the naked eye on close examination.


text:
Was the P-82 twin Mustang better than the P-51D?
The P-82 twin Mustang was made to replace the P-51D in the escort role. It was faster, and had two engines with two pilots. It also had a better armament but wasn't as maneuverable as the P-51D. Which would usually win in a dogfight and what plane did pilots prefer?

This'll prolly get closed as opinion based. In general, speed is paramount. If I had to fight Japanese Zeros in 1943, I'd want to be in a P-38, which couldn't maneuver with one, but was nearly a 100 mph faster and could outrun a Zero with ONE ENGINE FEATHERED. The faster plane can choose when to engage and disengage, and all other features are secondary to that. So if I had to choose between a better dogfighter and a significant speed advantage, speed is life. The P-82 was about 40 mph faster then the best Japanese fighter, the Ki-84. Two pilots addressed a big fatigue problem.

@JohnK  A friend used to describe dogfighting in an F-111 as:  Throttles - Full A/B, Wings - Full aft, Put it on the deck, Wave goodbye.

The two planes serve very different roles. The 82 was a long distance aircraft first and foremost, and everything else was secondary to that goal. The 51 was a fighter, and its excellent range was not a specific design criterion, but the result of several unrelated design decisions that worked in happy concert.
So, based on that alone, I think the answer is clear.
But the real issue with this comparison is the time dimension, the 82 saw combat when it was already outdated, whereas the 51 saw combat when it was the pinnacle of performance. Jets were already the hotness when the 82 was on the front line, and I doubt anyone looked favorably on being assigned to them when the alternative was an 84 or 86.


text:
What are the effects of separation at hypersonic rarefied flows?
Shock wave causes an adverse pressure gradient which causes an airfoil to stall. Also because gas density is much lower boundary layer becomes laminar and unable to prevent separation.
Correct me if information above is incorrect. Also are there any sources of stall? Like how much AoA affect separation? Can an airfoil stall (just because of hypersonic rarefied conditions) at 0° AoA?

Hypersonic rarified conditions means you're almost in space.
You are asking can you stall? Maybe the first question should be can you fly?
Correct me if I'm wrong but it seems that you are trying to apply a real life exemple to a totally different area of flight. The stall you are referring to happens in transonic flight when the shock wave appearing on the extrados forces the flow to detach.
In subsonic/transonic flight lift is generated through an acceleration of the flow around the extrados resulting in a pressure loss on the succion side of your wing. If the flow detach you're losing this acceleration effect of the flow following the surface of the wing and thus you lose lift.
In supersonic flight the shock waves starts attached to the leading edge of the wing. The shock deviates instantly the flow and the more the flow needs to be deviated the stronger the shock and the more pressure increases. Lift is generated through the difference of deviation in the flow betew intrados and extrados resulting in pressure difference on both side. The boundary layers here doesn't play a huge role and I've never heard of supersonic flight stall.
In hypersonic rarefied condition the shock detach from the body and you have very high temps, and complexe chemistry hapenning inside the layer between the shock and your surface thus making the flow hard to simulate. First of all you don't really use wings in this mixture of high energetic particles so speaking of stall doesn't make sens. Then lift is mostly done the same way as in supersonic, through the differential increase of pressure being the shock but the chemistry between the few molecules of air can create weird stuff resulting for exemple in asymmetrical lift on a surface for very complexe not always well known reason.

Maybe the OP has thought up a design where part of the airflow over the aircraft is still subsonic even when the aircraft is moving at over mach 5?  :-P

I guess you got a few things confused.
Rarefied flows are characterized by long distances between molecular collisions compared to the gradients of speed or pressure, so the molecules will not settle at the equilibrium limit. More precisely, the Knudsen number – defined as the ratio of the mean free path to some characteristic length – is greater than that required to approximate the flow as a continuous medium.
There are two possible conditions for rarefied flows:

Either flight in near-space (or conditions in near vacuum such as in chemical vapor deposition) where gas density is extremely low, or
flow inside conditions with extremely high gradients, such as in thin shock and boundary layer regions (like in the small gap between a hard disk and its magnetic head).

Next, you mention shock-induced stall. So I assume you mean the second condition. But that doesn't happen in hypersonic flow, but in transsonic flow when only some region of the flow field is supersonic (but most is still subsonic). Hypersonic rarefied flows (which can be found in reentry vehicles in the upper atmosphere) have no such thing as attached or separated flow, because these terms can only meaningfully be used for continuum flows.

Like how much AoA affect separation? Can an airfoil stall (just because of hypersonic rarefied conditions) at 0° AoA?

We have many questions here covering separation and stall angle of attack, all of which will tell you that separation depends less on AoA but pressure gradients.


text:
The meaning of "fully paid"
What is the meaning of "fully paid" in the airline industry? Based on my research it's an adjective and it means "paid for at full face value with no further money due from the stockholder", but I found the following sentence in this link where a poster uses it as a noun. if I have asked the question on the wrong forum, I apologize and please let me know. Thank you.
"WestJet service centre and was told they changed our fully paid for flights to one a day later."

In this context, I don't think it's a noun; I believe it's describing "flights." The poster here is saying that they had booked flights, the flights were fully paid for, and the airline changed the date for whatever reason.
The poster likely added "fully paid for" to emphasize that they had completed the transaction and purchased the flights before the date was changed. The exact point when that happens could be complicated to describe because of the vagaries of airline ticketing systems, but a consumer will typically view their flight as fully paid for once they've finished purchasing the tickets or at least once they've received an email confirmation of their booking.

In the rainy season in Bolivia your fully-paid-for flight might actually finally take place a week or more after the contracted date.

Thank you so very much for your explanation!


text:
Was flying a helicopter below building height against FAA regulations?
I'm referring to this incident: https://twitter.com/Dacheslow/status/1267638389421072384
Some people were saying it was illegal under FAA rules to fly that low and close to a crowd, and also to use a medical-designated helicopter to carry out police activity. Can anyone weigh in?

I don’t know exactly where in DC that happened, though I would say it’s highly probable that it was a public or law enforcement helicopter, or a lifeflite helo as virtually nothing else is allowed to fly VFR in the FRZ over DC without a lot of planning and waivers.
Helicopters, under general operation, are going to have to conform with §91.119(a), (d)(1), which state you must operate the helicopter at an altitude that, if a power unit were to fail, a landing can be made without creating an undue hazard to persons or property on the surface.  In the case of the helo in question, it’s a Eurocopter EC 135, which is a multi engine aircraft.  I don’t have the performance charts for that helo handy, but I believe it either can hover OGE or perform and aurtorotation landing at near standstill should an engine fail.
There’s also the fact that, as many cities right now are under a state of emergency, public vehicles may be forgoing a lot of regulations on flight ops for that reason.  The helo may also be looking for a place to land and hoping the people below can make a space for it.  I’m not sure here.

It's a military helicopter, it isn't subject to FAA regulations...

Police helicopters are also not subject to FAA regulations.

That’s false they both use the national airspace system, and while they do have certain operations that allow them extensions, they are both required to follow NAS rules.

To add more detail to Carlo Felicione’s answer and Ron Beyer’s comment, Part 91.119(d)(1) states, “A helicopter may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section [Minimum safe altitudes: General], provided each person operating the helicopter complies with any routes or altitudes specifically prescribed for helicopters by the FAA”.
So yes, helicopters can fly below the level of buildings, and do so more than people realize. The trick is to get clearance from ATC only in areas that would require such clearance.
Someone else may want to weigh in on the use of aircraft marked for medical use in police activities. I can not find anything in FAA regulations to prohibit this. I doubt that there is anything in international regulations to prohibit police use like there is for using it as a military combatant.
Using military equipment designated for the National Guard gets around any provision of the Federal Posse Comitatus Act. Also, the President can invoke The Insurrection Act of 1807 to mobilize federal and federalized troops when deemed necessary.


text:
What is relation between Reynolds number-turbulent flow-flow separation?
can some explain conection betwen re number -turbulent flow -and flow separation ,in example at wing in the air and water?
1)does high numbers= turbulent flow mean higher resistance to flow separation and low numbers=laminar flow less resitance to flow separation?
(becuase we use vortex generator to make trubulent flow which delay flow separation on upper wing surface...)
2)why L distance of chord has something with which type of flow will be over wing?
so wide chord will have more turbulent flow but it will delay flow separation?
3)in formula i see density and velocity in numerator,so high density and speed will delay flow separatin compare to lower density and lower speed?

I realize English is not your first language, but proper punctuation and capitalization is a thing in most languages, and would help make this question more readable.

so nobody answer?

What is the effect of airflow speed on separation?

@mins,isnt speed increase adrverse pressure gradient which will cause flow separation.so we cant say that with with speed we will dealy flow separation because of  higher Re. numbers?

@AeronauticFreek: Separation occurs because of the higher static pressure / lower kinetic pressure encountered while moving downstream within the boundary layer (adverse gradient due to viscosity and leading to deceleration). Lower kinetic pressure happens at lower relative speed / Re. Higher relative speed / Re translates (rather than increases, the gradient is along the chord) the adverse gradient downstream along the chord, delaying flow separation. So higher Re delays separation.

In most commercial aircraft applications the Reynolds number per foot of chord length lies between 1.5 and 2 million per foot. Major operations of takeoff and cruise for turboprop and turbofan airliners fall in this range. Consider the following mean aerodynamic chords:

Turboprop Aircraft = 6.9 ft < cMAC < 10.6 ft
= Reynolds number of 10-20 million

Turbofan Airliners = 13.3 ft < cMAC < 26.9 ft
= Reynolds number of 20-54 million

B747/A380 size Aircraft = 30.6 ft < cMAC < 40.33 ft = Reynolds number of 45-80 million

Note that for highly tapered wings the outboard chords may be considerably smaller than the mean aerodynamic chord and will experience lower Reynolds numbers. During low-speed operations like landing and takeoff, high lift devices such as flaps and slats must be used, because the characteristic lengths of these elements are considerably smaller than the local wing chord they will be operating at lower Reynolds number and therefore more susceptible to flow separation and stalling. The general trend is for cl,max to increase slowly, if at all, with increases in Reynolds number and for that increase to be more substantial for thicker sections. This is understandable because as the Reynolds number increases the boundary layer effects become relatively weaker allowing the flow to remain attached to the airfoil for longer distances along the airfoil surface. The lift of an airfoil depends primarily on keeping the flow attached to the airfoil while friction drag itself weakly influences the lift of an airfoil.
A more detailed explanation is available here


text:
What are the forces present in a coordinated turn?

During straight and level flight, coordinated flight is assumed when there is no net lateral force (no slip or no skid). But this concept totally breaks down when it comes to turning, in a co-ordinated or unco-ordinated turn; there will always be a net lateral force due to centripetal force provided by the horizontal component of the lift force. The centrifugal force (inertial force) found in the books, in an attempt to explain it doesn't make sense to me as the centrifugal force is an imaginary force. So how is co-ordinated flight achieved in term of the forces?
Thanks in advance.

Centrifugal force exists in the reference frame of the aircraft. If you do the analysis there, you need it, if you are doing it in the reference frame of the air, you don't. Since General Relativity, inertial forces are now considered just as real as any other forces, and include gravitational force, which by principle of equivalence (the core postulate of GR) is locally indistinguishable from acceleration of the reference frame. Note I didn't say gravity, because gravity actually means sum of all inertial forces (includes centrifugal force due to Earth rotation).

… doing analysis in the aircraft frame of reference is usually a bit nicer since there aircraft is stationary so all the aerodynamic and inertial forces cancel out. Plus it tells you what you'd feel if you were sitting in the aircraft, because you feel exactly the sum of inertial forces (a.k.a local gravity; includes gravitational forces). Of course the inertial forces just correspond to the acceleration as viewed from the reference frame of air, but since that frame is not in free fall, there are still some inertial forces and you have a more cases than in the aircraft one.

Oh boy, here we go again...

related: What does the balance ball actually indicate? and Is this vector diagram of the forces at play in turning flight correct?

Maybe this will inspire me to draw those diagrams...

I don't understand exactly what the question is.  Is the question "is it true that "centrifugal force" is only valid from the standpoint of an accelerated reference frame, such as the aircraft reference frame"?  Or is the question perhaps "How can we explain why the ball stays centered in a coordinated turn, from the standpoint of an unaccelerated reference frame, such as the airmass reference frame"?  Or do you just want a listing of all the forces present in a turn?  If so, in which reference frame?  The aircraft reference frame, the airmass reference frame, or both?

The diagrams you posted are incorrect and misleading because they don't explicitly include the aerodynamic sideforce generated by -- or more accurately, causing-- a slip or skid.  Par for the course though; such diagrams are very common.  Just out of curiousity, from what source do they come from?

Lets make this interesting: "What are the forces present in a coordinated turn in steady wind?". Sorry, could not help myself...

To get a deeper understanding beyond the superficial, it helps to break down the forces and moments present on an aircraft that may affect its rigid-body motion:

Aerodynamic forces: These are the forces and moments exerted by the airflow on the aircraft

Ground forces: These are the forces and moments exerted by the ground on the aircraft, transmitted through tyres and landing gear. Not applicable when it's flying.

Propulsion: Forces and moments due to direct thrust. For simplification, let's assume that thrust acts inline with the forward axis.

Gravitational forces: Gravity pulls the aircraft towards the ground. It's rather special because everything, be the aircraft structures, you, me, or the accelerometers, get pulled at the same rate ($g$)1. This is distinctly different than the other two types of forces, which are only present when airflow affects exposed areas, or when contact with the ground has been made.

Inertial forces: These are fictitious forces and moments that are required to maintain non-uniform motion. This includes your centripetal force. Inertial forces must always be equal to the sum of all the aforementioned external forces.

First of all, let's consider any turn a steady-state maneuver (thereby ignoring the transients like rolling in and rolling out), which means that the vector sum of all the external forces, including gravity, must sum to the inertial forces. As you've correctly pointed out, the sum of aerodynamic forces + gravitational forces must be equal to the centripetal force, which in the turning plane is provided by lift, side force and gravity. This must hold true for any steady-state turn, whether coordinated or not.

There are two ways to define a coordinated turn. With all engines operating, they are approximately equivalent:

A zero-sideslip turn
A ball-centered turn: we are going to use this definition

What ball-centered means is that there are no aerodynamic forces acting laterally on the airplane: lift must provide all the centripetal force required. Ball centered provides the best average feel for the occupants, since the forces are directly inline with the floor, and there's no side force causing sway. Since everything feels gravity at the same rate, occupants or the ball cannot detect gravity.
For illustration:

For the more math oriented, in inertial frame, Newton's second law is stated as:
$$\vec{F_{i}}+m\vec{g_i}=m\frac{d\vec{V_i}}{dt} \tag{1}$$
The entire right hand side is considered to be inertial forces. However, if the measurements occur in a rotating frame (on an airplane, for example), then we need to express everything into the body frame. The left-hand side is easy:
$$\vec{F_{b}} = C_{bi}\vec{F_{i}} \tag{2}$$
$$\vec{g_b} = C_{bi}\vec{g_i} \tag{3}$$
where $C_{bi}$ is the rotation matrix transforming a vector from inertial frame to body frame.
The right-hand side requires some adjustments, because the Euler angles of the body themselves are changing:
$$\frac{d\vec{V_b}}{dt}=\frac{d(C_{bi}\vec{V_i})}{dt}$$
Apply chain rule, and we have:
$$\frac{d\vec{V_b}}{dt}=\frac{dC_{bi}}{dt}\vec{V_i}+C_{bi}\frac{d\vec{V_i}}{dt} \tag{4}$$
It can be mathematically shown the following identity:
$$\frac{dC_{bi}}{dt}\vec{V_i} = -\vec{\omega_b} \times \vec{V_b} \tag{5}$$
Substitute (5) into (4), and we get:
$$C_{bi}\frac{d\vec{V_i}}{dt} = \frac{d\vec{V_b}}{dt} + \vec{\omega_b} \times \vec{V_b}$$
Finally, if we multiply both sides of (1) by $C_{bi}$ and simplify with (2), (3) and (5), we get:
$$\vec{F_{b}}+m\vec{g_b}=m \left( \frac{d\vec{V_b}}{dt}+\vec{\omega_b} \times \vec{V_b} \right) \tag{6}$$
(6) is the Newton's second law in a rotating frame. The entire right-hand side are still inertial forces (same as (1)), except now we also have the cross-product, which produces the centripetal inertial forces:
$$\vec{\omega_b} \times \vec{V_b} = \begin{bmatrix}p \\ q \\ r\end{bmatrix} \times \begin{bmatrix}u \\ v \\ w\end{bmatrix} = \begin{bmatrix} qw - rv \\ ru - pw \\ pv - qu \end{bmatrix} \tag{7}$$
You will readily identify terms like $ru$, which is very close to the familiar $a_c=\omega V$ for a restricted 2D centripetal motion (whence $p=0$ and $q=0$).
One final note, the right-hand side is fictitious in that they are not real forces! They are a result of the kinematic motion itself, and must require the left-hand side (which are the real forces), to sustain.

1: Technically, this is only true locally, because Earth is a sphere and does not exert a uniform field at different altitudes. But at the range of altitudes that airplanes will be flying, this is a rather good approximation.

Comments are not for extended discussion; this conversation has been moved to chat.

It is helpful to understand a basic concept in Physics to understand this. The answer to this depends on what frame of reference you are measuring things in. In what is called an "Inertial" frame of reference, only "real" forces need be considered, as only "real" forces cause acceleration (F=ma). In an inertial frame of reference the only real forces acting on an aircraft are the aerodynamic force (the pressure of the atmosphere on every square inch of the surface of the airframe), and the thrust produced by the engines. PERIOD.
But we all eat, sleep, walk, and fly on the surface of the earth, which is an accelerated frame of reference, due to the acceleration of Gravity, the rotation of the earth, the motion of the earth around the sun, etc. etc., and in that accelerated frame of reference, in order to explain the apparent motion of any body, other "fictitious" forces, such as *centrifugal force, the force of gravity itself, and other inertial forces, must all be considered to make the math work out. (In other words, as mentioned in another answer, to make the forces cancel out when the aircraft is in a "steady state").

*Note: Centrifugal force is often added on diagrams of aircraft in turns to help explain the apparent "balance" of forces for the
aircraft that is stable in the diagram. But the force, and the
"stability" are both fictitious, because the diagram is depicted in a
turning and rotating frame of reference.

Basically, these fictitious forces must be added in to "subtract out" the acceleration of the frame of reference itself, because without considering them, the answer you get would only be calculating the acceleration of the aircraft within an inertial (zero-G) frame of reference, and we generally want to know our acceleration in the frame we are otherwise examining (generally the earth-frame).

Re "Basically, these fictitious forces must be added in to "subtract out" the acceleration of the frame of reference itself... and we generally want to know our acceleration in the earth-frame."-- this answer might be a bit more clear if it explained that to calculate the acceleration in the earth-frame (or the airmass frame), the only "fictitious" force that must be added is gravity, not the "centrifugal force" that we typically see included in diagrams in flight training manuals.  These diagrams are typically based on the aircraft reference frame, not the ground or airmass reference frame.

(Which is why they have no explanatory power.  The only thing they really "explain" is that the apparent net force as seen from the aircraft reference frame is always zero.  They don't actually explain why the ball sits where it does in a skidding or slipping turn.)

@quiet flyer, I only mention centrifugal force as a "fictitious" force because I have seen documents and texts with diagrams that attempt to explain the balance of forces in turns, coordinated and uncoordinated, where the diagram is done in the frame of reference of the aircraft itself, which, obviously, IS an accelerated frame of reference.

I have edited my answer to make this clear.


text:
Has a civil aviation accident ever involved more than two manned aircraft?
Has a civil aviation accident ever involved more than two manned aircraft? Meaning, in one accident: more than two manned aircraft had fatalities or serious injuries or significant damage; or one or two manned aircraft had fatalities or serious injuries or significant damage, while other manned aircraft contributed to the accident, totaling three or more aircraft.
If military aircraft were involved, that would also be of interest, as long as at least one aircraft was civil aviation.

This would only happen when one hits the other two on the ground.

The Ramstein Airshow Disaster comes to mind, where one airplane of the Italian Air Force display team collided with 2 others during a display, so 3 airplanes were involved in the collision in the air. A medivac helicopter on the ground was also destroyed, which was manned at the time, fatally injuring the pilot.

This is very good info. But is it considered civil aviation?

No, but there were many civilian deaths,  and the question said if military aircraft were involved it would be of interest.

I found a case of an aircraft crashing into a hangar, damaging two more aircraft, bringing the total to three.

The Federal Aviation Administration said the plane had just taken off for St. Petersburg, Florida, when it crashed into the private hangar. There was no one inside the hangar at the time of the crash, but two aircraft, a helicopter and a jet were damaged, Landsberg said.

Source
Surely there have been similar accidents with more material damage.

If nobody was inside the hangar, how can the two aircraft damaged inside it be manned?


text:
Does the pilot flying always listen to radio communications?
When there is a pilot flying (PF) and a pilot monitoring (PM), does the PF always listen to flight deck radio communications? I would think Yes under normal conditions, but optionally No during emergencies, to reduce the PF's workload. Are there general guidelines for when the PF should or should not listen to radio communications, including listening to whatever the PM is saying on the radio?

A fundamental aspect of Crew Resource Management is that both crew are fully aware of everything that is happening in the flight deck so that they can continuously cross check each others' actions, to the extent that they can, to catch errors.
This goes double during emergencies. So the PF will be listening in on coms (although he/she may be tuning them out during intense stress - and the PM should be aware of that possibility) when they are not listening or communicating with someone else, such as a Flight Attendant, or a separate ATC frequency for whatever reason, or Company frequency (although this would be after the emergency drills are done).
During the peak workload part of an emergency, there shouldn't be any radio communication going on anyway other than the PM selecting 7700 and possibly making a Mayday announcement and to standby, if they can fit all that in (if an engine quits at rotation, likely nobody will be talking to ATC at all until the airplane is squared away or there is some break in the action). It's priority Number 3 in the Aviate, Navigate, Communicate meme after all.